I haven't used their treadmill, however the execs at a former employer had a couple of the Peloton bikes installed in our gym and I must say that they were a revelation compared to the standard bikes seen in most gyms today. Normally I climb aboard and get immersed in either television or an audiobook, but Peloton's bikes are more like a high end arcade game played/raced live against others around the world. Needless to say, they held my attention 30+ mins daily for over a year while working there, and I'd own one if I could justify the cost as a non-bicyclist.
As to the treadmill design, I dont see anything mechanically different in theirs vs many others. The track being open in back is common. I suspect this is simply another instance of an enormously popular/wealthy company being targeted by lawyers. Personally I have fallen several times on treadmills at the gym so can attest that it hurts and there is indeed a lot of potential for harm, but that's workout equipment in general. Small kids arent allowed in gyms for that exact reason, so no way in hell should a responsible adult allow them around it at home. Locking out a treadmill is easy, pull the magnetic switch and kids cant start it - 1/2 second's effort toward safety.